Yorkies can be too delicate for a 6 year old, especially a boy. I say, go for the Shi-tzu. My sister in law has one (and a 6 year old boy, to boot!) and he's great with the kids, and the kids are good with him. Shi-tzus are a little sturdier than Yorkies, and grow a little bigger (but no so big they can't be house-only dogs.)
